Process for producing water-soluble carboxylated polymer

ABSTRACT

A process for preparing a water-soluble carboxyl group-containing polymer comprising reacting an α,β-unsaturated carboxylic acid with a compound having at least two ethylenically unsaturated groups in an inert solvent in the presence of a radical polymerization initiator, the process for preparing a water-soluble carboxyl group-containing polymer being characterized in that the α,β-unsaturated carboxylic acid is further added to a reaction mixture in which 20 to 70% by mol of an unreacted α,β-unsaturated carboxylic acid remains, and the α,β-unsaturated carboxylic acid is reacted with the compound having at least two ethylenically unsaturated groups; and a water-soluble carboxyl group-containing polymer obtainable by the above-mentioned process, wherein the reducing ratio of viscosity of a 0.2% by weight neutralized viscous liquid is less than 25%, and the equilibrium viscosity of the neutralized viscous liquid is 20000 to 50000 mPa·s. The water-soluble carboxyl group-containing polymer obtainable by the present invention can be suitably used as a thickener for cosmetics and the like, a moisturizer for poultices and the like, an emulsifier, or a suspension stabilizer for suspensions, and the like.

TECHNICAL FIELD

The present invention relates to a process for preparing a water-solublecarboxyl group-containing polymer. More specifically, the presentinvention relates to a process for preparing a water-soluble carboxylgroup-containing polymer which can be suitably used as a thickener forcosmetics and the like, a moisturizer for poultices and the like, anemulsifier, or a suspension stabilizer for suspensions, and the like.

BACKGROUND ART

As a water-soluble carboxyl group-containing polymer, there have beenknown, for instance, a copolymer of an α,β-unsaturated carboxylic acidsuch as acrylic acid and a polyallyl ether (U.S. Pat. No. 2,923,692); acopolymer of an α,β-unsaturated carboxylic acid and hexaallyltrimethylene trisulfone (U.S. Pat. No. 2,958,679); a copolymer of anα,β-unsaturated carboxylic acid and triallyl phosphate (U.S. Pat. No.3,426,004); a copolymer of an α,β-unsaturated carboxylic acid andglycidyl methacrylate (Japanese Patent Laid-Open No. Sho 58-84819); acopolymer of an α,β-unsaturated carboxylic acid such as acrylic acid andpentaerythritol allyl ether (U.S. Pat. No. 5,342,911, No. 5,663,253 andNo. 4,996,274); a copolymer of an α,β-unsaturated carboxylic acid suchas acrylic acid, a (meth)acrylic acid ester and pentaerythritol allylether (Japanese Examined Patent Publication No. Hei 5-39966 and No. Sho60-12361); and the like. These water-soluble carboxyl group-containingpolymers have been used for uses such as a thickener for cosmetics, amoisturizer for poultices and the like, an emulsifier, or a suspensionstabilizer for suspensions and the like, after these water-solublecarboxyl group-containing polymers are dissolved in water and thesolution is neutralized with an alkali, to give a neutralized viscousliquid.

In order to use the above-mentioned water-soluble carboxylgroup-containing polymer for these uses, it is necessary to prepare aneutralized viscous liquid by firstly preparing a homogeneous aqueoussolution of the water-soluble carboxyl group-containing polymer, andthereafter neutralizing the aqueous solution with an alkali. However,since the above-mentioned water-soluble carboxyl group-containingpolymer is usually in the form of fine powder, a lump of powder tends tobe formed when the polymer is dissolved in water. Once the lump ofpowder is formed, a gel-like layer is formed on the surface of the lump.Therefore, there is a defect that the speed of penetrating water intothe interior of the lump is delayed, thereby making it difficult toobtain a homogeneous aqueous solution.

Therefore, when the aqueous solution of the water-soluble carboxylgroup-containing polymer is prepared, there is necessitated a procedurewith a poor production efficiency such that powder of the water-solublecarboxyl group-containing polymer is gradually added to water underhigh-speed agitation in order to prevent the formation of the lump ofpowder. In some cases, there is necessitated a specialized dissolutionapparatus in order to prevent the formation of the lump of powder.

On the other hand, in the field of cosmetics and the like, theabove-mentioned water-soluble carboxyl group-containing polymer isdissolved under a high-speed agitation, and thereafter the solution isneutralized with an alkali to give a neutralized viscous liquid, and ahigh-speed agitation is further continuously carried out in order toobtain a smoother gel appearance of a neutralized viscous liquid.However, when the high-speed agitation is maintained for a long periodof time, the viscosity of the neutralized viscous liquid is reduced dueto shearing during the agitation. Therefore, there is a defect that theabove-mentioned water-soluble carboxyl group-containing polymer has tobe used in a large amount for obtaining the same thickening effect.

An object of the present invention is to provide a process for preparinga water-soluble carboxyl group-containing polymer showing a smallreducing ratio of viscosity when prepared its neutralized viscous liquidand a high viscosity even at a low concentration, and being excellent intransparency and gel appearance (surface smoothness).

These and other objects of the present invention will be apparent fromthe following description.

DISCLOSURE OF INVENTION

The present invention relates to:

-   [1] a process for preparing a water-soluble carboxyl    group-containing polymer comprising reacting an α,β-unsaturated    carboxylic acid with a compound having at least two ethylenically    unsaturated groups in an inert solvent in the presence of a radical    polymerization initiator, the process for preparing a water-soluble    carboxyl group-containing polymer being characterized in that the    α,β-unsaturated carboxylic acid is further added to a reaction    mixture in which 20 to 70% by mol of an unreacted α,β-unsaturated    carboxylic acid remains, and the α,β-unsaturated carboxylic acid is    reacted with the compound having at least two ethylenically    unsaturated groups; and-   [2] a water-soluble carboxyl group-containing polymer obtainable by    the process of the above-mentioned [1], wherein the reducing ratio    of viscosity of a 0.2% by weight neutralized viscous liquid is less    than 25%, and the equilibrium viscosity of the neutralized viscous    liquid is 20000 to 50000 mPa·s.

BEST MODE FOR CARRYING OUT THE INVENTION

There is the greatest feature in the process for preparing awater-soluble carboxyl group-containing polymer of the presentinvention, that the process for preparing a water-soluble carboxylgroup-containing polymer comprises reacting an α,β-unsaturatedcarboxylic acid with a compound having at least two ethylenicallyunsaturated groups in an inert solvent in the presence of a radicalpolymerization initiator, and that the α,β-unsaturated carboxylic acidis further added to a reaction mixture in which 20 to 70% by mol of anunreacted α,β-unsaturated carboxylic acid remains, and theα,β-unsaturated carboxylic acid is reacted with the compound having atleast two ethylenically unsaturated groups.

The α,β-unsaturated carboxylic acids used in the present invention arenot limited to specified ones, and include, for instance,α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid,crotonic acid, maleic acid, itaconic acid and fumaric acid; alkyl estersof the α,β-unsaturated carboxylic acids having an alkyl group of 10 to30 carbon atoms, such as lauryl acrylate, myristyl acrylate, palmitylacrylate, oleyl acrylate, stearyl acrylate, behenyl acrylate, laurylmethacrylate, myristyl methacrylate, palmityl methacrylate, oleylmethacrylate, stearyl methacrylate and behenyl acrylate; and the like.These can be used alone as the α,β-unsaturated carboxylic acid, or theα,β-unsaturated carboxylic acid and the alkyl ester of theα,β-unsaturated carboxylic acid having an alkyl group of 10 to 30 carbonatoms can be simultaneously used. Among them, acrylic acid alone, or amixture of acrylic acid and lauryl methacrylate is favorably usedbecause it is inexpensive and readily available and gives excellenttransparency to the neutralized viscous liquid of the water-solublecarboxyl group-containing polymer.

It is desired that the amount of the α,β-unsaturated carboxylic acidused in the initial reaction is 6 to 25 parts by volume, preferably 8 to22 parts by volume, more preferably 13 to 20 parts by volume based on100 parts by volume of the inert solvent described later. It ispreferable that the amount of the α,β-unsaturated carboxylic acid is atleast 6 parts by volume from the viewpoint of giving excellenttransparency to the neutralized viscous liquid of the resultingwater-soluble carboxyl group-containing polymer. Also, the amount of theα,β-unsaturated carboxylic acid is at most 25 parts by volume from theviewpoint that the mixture can be homogeneously agitated even if thewater-soluble carboxyl group-containing polymer is precipitated as thereaction proceeds.

The compound having at least two ethylenically unsaturated groups usedin the present invention is not limited to specified ones, and includes,for instance, acrylates of polyols having at least two substitutedgroups such as ethylene glycol, propylene glycol, polyoxyethyleneglycol, polyoxypropylene glycol, glycerol, polyglycerol,trimethylolpropane, pentaerythritol, saccharose and sorbitol;methacrylates of polyols having at least two substituted groups; allylethers of these polyols having at least two substituted groups; diallylphthalate, triallyl phosphate, allyl methacrylate, tetraallyloxyethane,triallyl cyanurate, divinyl adipate, vinyl crotonate, 1,5-hexadiene,divinylbenzene, and the like. Among them, pentaerythritol tetraallylether, diethylene glycol diallyl ether or polyallyl saccharose isfavorably used from the viewpoint of being capable of obtaining aneutralized viscous liquid of the water-soluble carboxylgroup-containing polymer having high viscosity, and giving highsuspension stability to an emulsion, a suspension or the like.

It is desired that the amount of the compound having at least twoethylenically unsaturated groups used is 0.15 to 2 parts by weight,preferably 0.3 to 1.5 parts by weight based on 100 parts by weight ofthe initial α,β-unsaturated carboxylic acid. It is preferable that theamount of the compound having at least two ethylenically unsaturatedgroups used is at least 0.15 parts by weight from the viewpoint ofprevention from reducing viscosity of the neutralized viscous liquid ofthe resulting water-soluble carboxyl group-containing polymer. Also, itis preferable that the amount of the compound having at least twoethylenically unsaturated groups used is at most 2 parts by weight fromthe viewpoint of preventing the formation of an insoluble gel in theneutralized viscous liquid of the resulting water-soluble carboxylgroup-containing polymer.

The radical polymerization initiator usable in the present invention isnot limited to specified ones, and includes, for instance,α,α′-azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile,dimethyl-2,2′-azobisisobutyrate, benzoyl peroxide, lauroyl peroxide,cumene hydroperoxide, tertiary butyl hydroperoxide, and the like. Amongthem, α,α′-azobisisobutyronitrile is preferable from the viewpoint ofbeing easy to handle and excellent in stability.

It is desired that the amount of the radical polymerization initiatorused is 0.003 to 0.20 mol based on 100 mol of the initialα,β-unsaturated carboxylic acid. It is preferable that the amount of theradical polymerization initiator used is at least 0.003 mol based on 100mol of the initial α,β-unsaturated carboxylic acid, from the viewpointof maintaining an appropriate reaction rate and being economical. It ispreferable that the amount of the radical polymerization initiator usedis at most 0.20 mol based on 100 mol of the initial α,β-unsaturatedcarboxylic acid, from the viewpoint that heat removal is simplifiedwithout rapidly progressing the polymerization, and that the reactioncontrol is facilitated.

The inert solvent as used herein refers to a solvent which dissolves theα,β-unsaturated carboxylic acids and the compound having at least twoethylenically unsaturated groups but does not dissolve the water-solublecarboxyl group-containing polymer obtained.

The inert solvent includes, for instance, normal pentane, normal hexane,isohexane, normal heptane, normal octane, isooctane, cyclopentane,methylcyclopentane, cyclohexane, methylcyclohexane, benzene, toluene,xylene, chlorobenzene, ethylene dichloride, ethyl acetate, isopropylacetate, methyl ethyl ketone, methyl isobutyl ketone, and the like.These can used alone or in admixture of at least two kinds. Among them,normal hexane is favorably used from the viewpoint of having relativelylow influence to human bodies and being inexpensive and readilyavailable.

When the α,β-unsaturated carboxylic acid is reacted with the compoundhaving at least two ethylenically unsaturated groups, it is preferablethat the reaction is carried out in the presence of an alkali metalcarbonate together with the radical polymerization initiator. When theα,β-unsaturated carboxylic acid is reacted with the compound having atleast two ethylenically unsaturated groups in the presence of the alkalimetal carbonate together with the radical polymerization initiator asdescribed above, the gel appearance of the neutralized viscous liquid ofthe resulting water-soluble carboxyl group-containing polymer can beimproved.

The alkali metal carbonate includes sodium carbonate, potassiumcarbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, andthe like. Among them, sodium carbonate and potassium carbonate arefavorably used from the viewpoint that the reduction of the viscosity ofthe neutralized viscous liquid of the resulting water-soluble carboxylgroup-containing polymer is small.

It is desired that the amount of the alkali metal carbonate used is0.001 to 1 part by weight based on 100 parts by weight of the initialα,β-unsaturated carboxylic acid. It is preferable that the amount of thealkali metal carbonate used is at least 0.001 parts by weight from theviewpoint of being capable of improving the gel appearance of theneutralized viscous liquid of the resulting water-soluble carboxylgroup-containing polymer. Also, it is preferable that the amount of thealkali metal carbonate used is at most 1 part by weight from theviewpoint of maintaining the viscosity of the neutralized viscous liquidof the resulting water-soluble carboxyl group-containing polymer.

When the α,β-unsaturated carboxylic acid is reacted with the compoundhaving at least two ethylenically unsaturated groups, it is preferablethat the atmosphere is, for instance, an atmosphere of an inert gas suchas nitrogen gas or argon gas.

It is desired that the reaction temperature is 50° to 90° C., preferably55° to 75° C. It is preferable that the reaction temperature is at least50° C. from the viewpoint of suppressing the increase of the viscosityof the reaction mixture so that the reaction mixture can be agitatedhomogeneously. Also, it is preferable that the reaction temperature isat most 90° C. from the viewpoint of being capable of controlling thereaction without rapidly progressing the reaction. The reaction timecannot be absolutely determined because the reaction time differsdepending upon the reaction temperature. The reaction time is usually0.5 to 5 hours.

As mentioned above, in the present invention, the greatest featureresides in that the α,β-unsaturated carboxylic acid is further added toa reaction mixture in which 20 to 70% by mol, preferably 30 to 60% bymol, more preferably 30 to 50% by mol of the unreacted α,β-unsaturatedcarboxylic acid used in the initial reaction mixture remains, and theα,β-unsaturated carboxylic acid is reacted with the compound having atleast two ethylenically unsaturated groups. The amount of the unreactedα,β-unsaturated carboxylic acid is at least 20% by mol of theα,β-unsaturated carboxylic acid used in the initial reaction mixturefrom the viewpoint of making the reducing ratio of viscosity of theneutralized viscous liquid of the resulting water-soluble carboxylgroup-containing polymer small. Also, similarly, the amount of theunreacted α,β-unsaturated carboxylic acid is at most 70% by mol of theα,β-unsaturated carboxylic acid used in the initial reaction mixturefrom the viewpoint of making the reducing ratio of viscosity of theneutralized viscous liquid of the resulting water-soluble carboxylgroup-containing polymer small. Here, the unreacted α,β-unsaturatedcarboxylic acid can be determined by measuring the amount of theα,β-unsaturated carboxylic acid remaining in the reaction mixture withhigh-performance liquid chromatography.

The α,β-unsaturated carboxylic acid to be added may be the same compoundas or a different compound from the initial α,β-unsaturated carboxylicacid, and includes, for instance, α,β-unsaturated carboxylic acids suchas acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconicacid, fumaric acid; alkyl esters of the α,β-unsaturated carboxylic acidshaving an alkyl group of 10 to 30 carbon atoms, such as lauryl acrylate,myristyl acrylate, palmityl acrylate, oleyl acrylate, stearyl acrylate,behenyl acrylate, lauryl methacrylate, myristyl methacrylate, palmitylmethacrylate, oleyl methacrylate, stearyl methacrylate and behenylacrylate; and the like. These can be used alone as the α,β-unsaturatedcarboxylic acid, or the α,β-unsaturated carboxylic acid and the alkylester of the α,β-unsaturated carboxylic acid having an alkyl group of 10to 30 carbon atoms can be simultaneously used. Among them, acrylic acidalone, or a mixture of acrylic acid and lauryl methacrylate is favorablyused because it is inexpensive and readily available and gives excellenttransparency to the neutralized viscous liquid of the water-solublecarboxyl group-containing polymer.

It is desired that the amount of the α,β-unsaturated carboxylic acidadded is 3 to 60% by weight, preferably 5 to 50% by weight, morepreferably 10 to 40% by weight of the amount of the initialα,β-unsaturated carboxylic acid. It is preferable that the amount of theα,β-unsaturated carboxylic acid added is at least 3% by weight from theviewpoint of obtaining a water-soluble carboxyl group-containing polymerwhich gives a neutralized viscous liquid having a small reducing ratioof viscosity and being excellent in thickening property even at a lowconcentration and transparency. Also, it is preferable that the amountof the α,β-unsaturated carboxylic acid added is at most 60% by weightfrom the viewpoint that the mixture can be homogeneously agitated evenif the water-soluble carboxyl group-containing polymer is precipitatedas the reaction proceeds.

The α,β-unsaturated carboxylic acid may be added at a time, or in pluraldivided portions.

It is desired that the reaction temperature is 50° to 90° C., preferably55° to 75° C. when the α,β-unsaturated carboxylic acid is added toreact. In other words, the α,β-unsaturated carboxylic acid can befurther added at the temperature at which the α,β-unsaturated carboxylicacid is firstly reacted with the compound having at least twoethylenically unsaturated groups in an inert solvent in the presence ofa radical polymerization initiator. The reaction time after the additioncannot be absolutely determined because the reaction time differsdepending upon the reaction temperature. The reaction time is usually0.5 to 5 hours.

After the termination of the reaction, white fine powder of thewater-soluble carboxyl group-containing polymer can be obtained byheating the reaction mixture to 80° to 130° C. to remove the inertsolvent by evaporation. It is preferable that the heating temperature isat least 80° C. from the viewpoint of being capable of drying in a shortperiod of time. Also, it is preferable that the heating temperature isat most 130° C. from the viewpoint of being excellent in solubility ofthe resulting water-soluble carboxyl group-containing polymer.

It is desired that the reducing ratio of viscosity of a 0.2% by weightneutralized viscous liquid of the water-soluble carboxylgroup-containing polymer thus obtained is less than 25%, preferably lessthan 15%. It is preferable that the reducing ratio of viscosity of the0.2% by weight neutralized viscous liquid is less than 25% from theviewpoint of being capable of securing stable thickening property whencosmetics and the like are produced, and suppressing variance in qualityin industrial production. The reducing ratio of viscosity in the presentinvention refers to a value determined by the determination methoddescribed later.

In addition, it is desired that the equilibrium viscosity of a 0.2% byweight neutralized viscous liquid of the water-soluble carboxylgroup-containing polymer of the present invention is 20000 to 50000mPa·s, preferably 25000 to 40000 mPa·s. It is preferable that theequilibrium viscosity is at least 20000 mPa·s from the viewpoint ofbeing economical without increasing the amount of the water-solublecarboxyl group-containing polymer used for securing the same thickeningproperty. Also, it is preferable that the equilibrium viscosity is atmost 50000 mPa·s from the viewpoint that the amount of the water-solublecarboxyl group-containing polymer used is appropriate for securing thesame thickening property, and that the neutralized viscous liquid has along-term stability against a salt or light. The equilibrium viscosityin the present invention refers to a value determined by thedetermination method described later.

The process for preparing a neutralized viscous liquid using theresulting water-soluble carboxyl group-containing polymer is not limitedto specified ones. For instance, the water-soluble carboxylgroup-containing polymer is dissolved in water so as to have aconcentration of the polymer of 0.01 to 3% by weight, and thereafter thesolution is neutralized with an alkali such as an alkali metal hydroxidesuch as sodium hydroxide, or an amine such as triethanolamine ordiisopropanolamine so as to have a pH of 6.5 to 7.5.

The neutralized viscous liquid obtained by using the water-solublecarboxyl group-containing polymer of the present invention is lesslikely to be subjected to shearing during agitation and has a smallreducing ratio of viscosity. Also, since this neutralized viscous liquidhas a high viscosity even at a low concentration and is excellent intransparency and gel appearance, the properties of cosmetics and thelike can be well maintained.

The reason why the water-soluble carboxyl group-containing polymerobtained by the process of the present invention has excellentproperties as described above are not explicit. The reason can bepresumed to be as follows: Specifically, in an ordinary process, thereis obtained a water-soluble carboxyl group-containing polymer having athree-dimensional structure in which polymer chains grown from manycross-linking points are entangled. On the other hand, according to theprocess of the present invention, it is thought that there is obtainedby further adding the α,β-unsaturated carboxylic acid, which is amonomer, at a specific polymerization stage, a water-soluble carboxylgroup-containing polymer having a three-dimensional structure in whichnew polymer chains are entangled on the surface of the three-dimensionalstructure in which polymer chains grown from the above-mentioned manycross-linking points are entangled. Therefore, it is thought that thereducing the viscosity of the neutralized viscous liquid which is causedby loosening the polymer chains entangled to each other due to shearingduring the agitation is less likely to take place, and that theneutralized viscous liquid has a high viscosity even at a lowconcentration.

The present invention will be explained more specifically hereinbelow bymeans of examples and comparative examples, without intending to limitthe present invention only to these examples.

EXAMPLE 1

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.2 g (0.0008 mol) of laurylmethacrylate, 0.08 g of sodium carbonate, 0.25 g of pentaerythritoltetraallyl ether, 0.16 g (0.001 mol) of α,α′-azobisisobutyronitrile and177 g (264 mL) of n-hexane. Subsequently, the mixture was homogenouslymixed with stirring, and thereafter nitrogen gas was blown into thesolution in order to remove oxygen existing in the upper space of theflask, the starting materials and the solvent. Next, the temperature ofthe mixture was kept at 60° to 65° C. for 1 hour under nitrogenatmosphere to react. The total amount of unreacted acrylic acid andlauryl methacrylate in the reaction mixture at that time was 0.230 moland 41% by mol of the total amount of charged acrylic acid and laurylmethacrylate.

Subsequently, 10 g (0.14 mol, 9.5 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 3 hours at thesame temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 48 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

EXAMPLE 2

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.08 g of potassium carbonate, 0.48 g ofdiethylene glycol diallyl ether, 0.16 g (0.001 mol) ofα,α′-azobisisobutyronitrile and 177 g (264 mL) of n-hexane.Subsequently, the mixture was homogenously mixed with stirring, andthereafter nitrogen gas was blown into the solution in order to removeoxygen existing in the upper space of the flask, the starting materialsand the solvent. Next, the temperature of the mixture was kept at 60° to65° C. for 1.5 hours under nitrogen atmosphere to react. The amount ofunreacted acrylic acid in the reaction mixture at that time was 0.174mol and 31% by mol of the amount of charged acrylic acid.

Subsequently, 10 g (0.14 mol, 9.5 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 2.5 hours atthe same temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 48 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

EXAMPLE 3

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.2 g (0.0008 mol) of laurylmethacrylate, 0.08 g of sodium carbonate, 0.25 g of pentaerythritoltetraallyl ether, 0.16 g (0.001 mol) of α,α′-azobisisobutyronitrile and177 g (264 mL) of n-hexane. Subsequently, the mixture was homogenouslymixed with stirring, and thereafter nitrogen gas was blown into thesolution in order to remove oxygen existing in the upper space of theflask, the starting materials and the solvent. Next, the temperature ofthe mixture was kept at 60° to 65° C. for 1 hour under nitrogenatmosphere to react. The total amount of unreacted acrylic acid andlauryl methacrylate in the reaction mixture at that time was 0.230 moland 41% by mol of the total amount of charged acrylic acid and laurylmethacrylate.

Subsequently, 16 g (0.22 mol, 15.2 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 3 hours at thesame temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 55 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

EXAMPLE 4

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.25 g of pentaerythritol tetraallylether, 0.16 g (0.001 mol) of α,α′-azobisisobutyronitrile and 177 g (264mL) of n-hexane. Subsequently, the mixture was homogenously mixed withstirring, and thereafter nitrogen gas was blown into the solution inorder to remove oxygen existing in the upper space of the flask, thestarting materials and the solvent. Next, the temperature of the mixturewas kept at 60° to 65° C. for 1.5 hours under nitrogen atmosphere toreact. The amount of unreacted acrylic acid in the reaction mixture atthat time was 0.174 mol and 31% by mol of the amount of charged acrylicacid.

Subsequently, 10 g (0.14 mol, 9.5 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 2.5 hours atthe same temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 48 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

EXAMPLE 5

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.2 g (0.0008 mol) of laurylmethacrylate, 0.25 g of pentaerythritol tetraallyl ether, 0.16 g (0.001mol) of α,α′-azobisisobutyronitrile and 177 g (264 mL) of n-hexane.Subsequently, the mixture was homogenously mixed with stirring, andthereafter nitrogen gas was blown into the solution in order to removeoxygen existing in the upper space of the flask, the starting materialsand the solvent. Next, the temperature of the mixture was kept at 60° to65° C. for 2 hours under nitrogen atmosphere to react. The total amountof unreacted acrylic acid and lauryl methacrylate in the reactionmixture at that time was 0.118 mol and 21% by mol of the total amount ofcharged acrylic acid and lauryl methacrylate.

Subsequently, 10 g (0.14 mol, 9.5 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 2 hours at thesame temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 48 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

COMPARATIVE EXAMPLE 1

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.08 g of sodium carbonate, 0.25 g ofpentaerythritol tetraallyl ether, 0.16 g (0.001 mol) ofα,α′-azobisisobutyronitrile and 177 g (264 mL) of n-hexane.Subsequently, the mixture was homogenously mixed with stirring, andthereafter nitrogen gas was blown into the solution in order to removeoxygen existing in the upper space of the flask, the starting materialsand the solvent. Next, the temperature of the mixture was kept at 60° to65° C. for 5 hours under nitrogen atmosphere to react.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 38 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

COMPARATIVE EXAMPLE 2

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.2 g (0.0008 mol) of laurylmethacrylate, 0.08 g of sodium carbonate, 0.25 g of pentaerythritoltetraallyl ether, 0.16 g (0.001 mol) of α,α′-azobisisobutyronitrile and177 g (264 mL) of n-hexane. Subsequently, the mixture was homogenouslymixed with stirring, and thereafter nitrogen gas was blown into thesolution in order to remove oxygen existing in the upper space of theflask, the starting materials and the solvent. Next, the temperature ofthe mixture was kept at 60° to 65° C. for 0.5 hour under nitrogenatmosphere to react. The total amount of unreacted acrylic acid andlauryl methacrylate in the reaction mixture at that time was 0.404 moland 72% by mol of the total amount of charged acrylic acid and laurylmethacrylate.

Subsequently, 2 g (0.03 mol, 1.9 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 3.5 hours atthe same temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 40 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

COMPARATIVE EXAMPLE 3

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser tube was charged with 40 g (0.56mol, 38.1 mL) of acrylic acid, 0.2 g (0.0008 mol) of laurylmethacrylate, 0.08 g of sodium carbonate, 0.25 g of pentaerythritoltetraallyl ether, 0.16 g (0.001 mol) of α,α′-azobisisobutyronitrile and177 g (264 mL) of n-hexane. Subsequently, the mixture was homogenouslymixed with stirring, and thereafter nitrogen gas was blown into thesolution in order to remove oxygen existing in the upper space of theflask, the starting materials and the solvent. Next, the temperature ofthe mixture was kept at 60° to 65° C. for 3.5 hours under nitrogenatmosphere to react. The total amount of unreacted acrylic acid andlauryl methacrylate in the reaction mixture at that time was 0.028 moland 5% by mol of the total amount of charged acrylic acid and laurylmethacrylate.

Subsequently, 26 g (0.36 mol, 24.8 mL) of acrylic acid was added theretoat the same temperature, and the mixture was reacted for 3 hours at thesame temperature.

After the termination of the reaction, the resulting slurry was heatedto 90° C. to distill off n-hexane, to give 64 g of a water-solublecarboxyl group-containing polymer in the form of fine white powder.

As physical properties of the water-soluble carboxyl group-containingpolymers obtained in Examples 1 to 5 and Comparative Examples 1 to 3,reducing ratio of viscosity, equilibrium viscosity, transparency and gelappearance of a 0.2% by weight neutralized viscous liquid of thewater-soluble carboxyl group-containing polymer were evaluated inaccordance with the following methods. The results are shown in Table 1.

(Evaluation of Physical Properties of Water-Soluble CarboxylGroup-Containing Polymer)

(1) Reducing Ratio of Viscosity and Equilibrium Viscosity

A 2-L glass beaker (diameter: 14 cm) was charged with 980 g ofion-exchanged water and 20 g of a water-soluble carboxylgroup-containing polymer, and the mixture was agitated with a high-speedagitator (T.K. HOMO DISPER f model; manufactured by TOKUSHU KIKA KOGYOCo. Ltd.) at 5000 rotations per minute for 3 minutes to dissolve thewater-soluble carboxyl group-containing polymer. The resulting solutionwas allowed to stand at 20° to 30° C. for 24 hours. Next, a 2-L glassbeaker (diameter: 14 cm) was charged with 100 g of the above-mentionedsolution which had been allowed to stand for 24 hours and 857 g ofion-exchanged water, and the mixture was agitated with the high-speedagitator at 2000 rotations per minute for 1 minute to homogenize theentire mixture. Subsequently, 43 g of a 2% by weight aqueous solution ofpotassium hydroxide was added thereto, at the same time, the rotationalspeed of the high-speed agitator was increased to 5000 rotations perminute, and the mixture was mixed with agitating for 2 minutes. Theviscosity of the obtained 0.2% by weight neutralized viscous liquid (pH6.8) was measured with a BL-type rotary viscometer under the conditionsof Rotor No. 4, 12 rotations per minute and a temperature of 25° C.(viscosity after 2 minute-agitation) after 30 seconds passed. Further,the liquid was mixed with agitating in the same manner for 13 minutes,and the viscosity was measured (viscosity after 15 minute-agitation).Reducing ratio of viscosity was calculated from the measured valuesobtained in accordance with the following equation. Also, theequilibrium viscosity was defined as the above-mentioned viscosity after15 minute-agitation.

[Reducing  ratio  of  viscosity] = {[Viscosity  after  2  minute-agitation − Viscosity  after  15  minute-agitation) ÷ (Viscosity  after  2   minute-agitation)]} × 100(2) Transparency

A cell of 1 cm×1 cm was charged with the neutralized viscous liquid ofthe water-soluble carboxyl group-containing polymer, the viscosity ofwhich had been measured after 15 minute-agitation, and the transmittancewas measured at a wavelength of 425 nm. When the transmittance is atleast 96%, the liquid can be usually evaluated to have excellenttransparency.

(3) Gel Appearance

The gel appearance of the neutralized viscous liquid of thewater-soluble carboxyl group-containing polymer was visually evaluated.The evaluation was made by a total of 10 male and female individuals asevaluation panelists, and the number of individuals of the panelists whohad an excellent feel for the evaluation on the gel appearance of theneutralized viscous liquid was totaled, and judged on the bases of thefollowing evaluation criteria. When the following judgment is at least ∘in the following evaluation criteria, the liquid can be usuallyevaluated to have an excellent gel appearance.

Evaluation Criteria

-   ⊚: the number of individuals who had a feel that the gel appearance    of the neutralized viscous liquid is excellent being 10-   ∘: the number of individuals who had a feel that the gel appearance    of the neutralized viscous liquid is excellent being from 8 to 9-   Δ: the number of individuals who had a feel that the gel appearance    of the neutralized viscous liquid is excellent being at most 7

TABLE 1 Viscosity (mPa · s) Reducing Agitation Time Ratio of 15Viscosity Transmittance Gel 2 minutes minutes (%) (%) Appearance Ex. 135000 31000 11.4 98 ⊚ Ex. 2 32000 27500 14.1 99 ⊚ Ex. 3 32000 30000 6.399 ⊚ Ex. 4 32500 28000 13.8 99 ◯ Ex. 5 32200 25000 22.4 97 ◯ Comp. 2800019000 32.1 95 Δ Ex. 1 Comp. 29500 20000 32.2 96 ◯ Ex. 2 Comp. 2300015000 34.8 97 Δ Ex. 3

It can be seen from the results shown in Table 1 that the reducing ratioof viscosity of the 0.2% by weight neutralized viscous liquids of thewater-soluble carboxyl group-containing polymers obtained in Examples 1to 5 are less than 25%, and that the equilibrium viscosities thereof arewithin the range from 20000 to 50000 mPa·s. On the other hand, it can beseen that the reducing ratio of viscosity of the 0.2% by weightneutralized viscous liquids of the water-soluble carboxylgroup-containing polymers obtained in Comparative Examples 1 to 3 are atleast 25%, and that the equilibrium viscosities thereof are at most20000 mPa·s. Also, it can be seen that the 0.2% by weight neutralizedviscous liquids of the water-soluble carboxyl group-containing polymersobtained in Examples 1 to 5 have a high viscosity even at a lowconcentration and are excellent in transparency and gel appearance.

INDUSTRIAL APPLICABILILTY

The neutralized viscous liquid of the water-soluble carboxylgroup-containing polymer obtained in the process of the presentinvention has a low reducing ratio of viscosity and a high viscosityeven at a low concentration, and is excellent in transparency and gelappearance. Accordingly, the water-soluble carboxyl group-containingpolymer obtained by the process of the present invention can be suitablyused as a thickener for cosmetics and the like, a moisturizer forpoultices and the like, an emulsifier, or a suspension stabilizer forsuspensions and the like, as compared with conventional polymers.

It is obvious that there are various kinds of equivalents which fallinto the same scope of the present invention described above. Suchvariations are not to be regarded as a departure from the purpose andscope of the invention, and all such modifications as would be obviousto those skilled in the art are intended to be included within thetechnological scope of the following claims.

1. A process for preparing a water-soluble carboxyl group-containingpolymer of which monomer composition consists essentially of anα,β-unsaturated carboxylic acid and a compound having at least twoethylenically unsaturated groups, said process comprising reacting theα,β-unsaturated carboxylic acid with the compound having at least twoethylenically unsaturated groups in an inert solvent in the presence ofa radical polymerization initiator, said process for preparing awater-soluble carboxyl group-containing polymer being characterized inthat the α,β-unsaturated carboxylic acid is further added to a reactionmixture in which 20 to 70% by mol of an unreacted α,β-unsaturatedcarboxylic acid remains, and the α,β-unsaturated carboxylic acid isreacted with the compound having at least two ethylenically unsaturatedgroups, wherein the α,β-unsaturated carboxylic acid is acrylic acid, ora mixture of acrylic acid and lauryl methacrylate, and wherein thecompound having at least two ethylenically unsaturated groups ispentaerythritol tetraallyl ether, diethylene glycol diallyl ether orpolyallyl saccharose.
 2. The process according to claim 1, wherein thereaction is carried out in the presence of an alkali metal carbonate. 3.The process according to claim 2, wherein the alkali metal carbonate issodium carbonate or potassium carbonate.
 4. A water-soluble carboxylgroup-containing polymer obtained by the process of any one of claims 1to 3, wherein the reducing ratio of viscosity of a 0.2% by weightneutralized viscous liquid of the water-soluble carboxylgroup-containing polymer is less than 25%, and the equilibrium viscosityof the neutralized viscous liquid is 20000 to 50000 mPa·s.
 5. A processfor preparing a water-soluble carboxylic group-containing polymer, saidpolymer being formed from monomers consisting essentially of aα,β-unsaturated carboxylic acid and a compound having at least twoethylenically unsaturated groups, said process comprising: (a) reactingthe α,β-unsaturated carboxylic acid and the compound having at least twoethylenically unsaturated groups in an inert solvent in the presence ofa radical polymerization initiator until a reaction mixture containing20 to 70% by mol of unreacted α,β-unsaturated carboxylic acid results;and (b) adding additional α,β-unsaturated carboxylic acid to thereaction mixture obtained from (a) to react with the compound having atleast two ethylenically unsaturated groups, wherein the α,β-unsaturatedcarboxylic acid is acrylic acid, or a mixture of acrylic acid and laurylmethacrylate, and wherein the compound having at least two ethylenicallyunsaturated groups is pentaerythritol tetraallyl ether, diethyleneglycol diallyl ether or polyallyl saccharose.
 6. The process accordingto claim 5, wherein an initial reaction mixture of (a) comprises (1) 6to 25 parts by volume of the α,β-unsaturated carboxylic acid based on100 parts by volume of inert solvent, and (2) 0.15 to 2 parts by weightof the compound having at least two ethylenically unsaturated groupsbased on 100 parts by weight of initial α,β-unsaturated carboxylic acid.7. The process according to claim 6, wherein the initial reactionmixture of (a) uses 8-22 parts by volume of the α,β-unsaturatedcarboxylic acid based on 100 parts by volume of inert solvent.
 8. Theprocess according to claim 6, wherein the initial reaction mixture of(a) uses 13-20 parts by volume of the α,β-unsaturated carboxylic acidbased on 100 parts by volume of inert solvent.